This invention relates to an apparatus and method for testing reflex action of the Achilles tendons of a human subject to aid in the detection and diagnosis of various disorders and diseases.
It is well established that abnormal reflex action, such as exaggerated, attenuated, or slow reflex actions, can be a symptom indicative of certain diseases, neurological damage, or other physiological disorders. Because of well recognized correlations between abnormal human reflex action and certain medical disorders, and because reflex testing is a relatively inexpensive and nonintrusive procedure for quickly determining whether a patient might be afflicted with such medical disorders, physicians commonly rely on reflex testing as a screening technique during routine physical examination of a patient, with more specific testing generally being recommended to verify or determine the specific disorder afflicting those patients which exhibit abnormal reflexes. Reflex testing is also conveniently used to track the progress of patients which have been diagnosed with, and are being treated for, a particular disease or disorder which affects the patient's reflexes.
In its original and simplest form, reflex testing of the Achilles tendons of a patient was conducted by merely striking the patient's tendon with a reflex hammer and visually observing the reflex action of the patient. A physician could also supplement visual observations with tactile perceptions such as by holding the patient's foot before striking the patient's tendon to sense the force of the reflex actions. Even for highly skilled and experienced physicians, the reliability of detecting abnormal reflexes using manual striking technique and unaided visual and tactile perceptions was not always satisfactory. Moreover, such testing procedures are generally useless for tracking a patient's progress such as to determine whether the patient is responding favorably to a particular treatment. The deficiencies of simple reflex testing procedures including manual striking and sensory observations include the inherent difficulty of striking a patient's Achilles tendon in the same place with the same amount of force for each test, and the difficult of judging whether a particular patient's reflex response deviates significantly from normal based on a comparison of the physician's visual and tactile observations of the patient's reflex response with the physician's memory of similar observations for a normal person.
In attempts to overcome the foregoing problems associated with manual reflex testing and unaided human sensory perception, and thereby improve the reliability and inherent utility of reflex testing, various devices have been developed for striking the Achilles tendon (or other selected portion of a patient's body) with an accurately reproducible, predetermined amount of force, and precisely at the desired position on the tendon, and various other devices have been developed for measuring and recording the reflex action induced by striking the Achilles tendon (or other portion of the patient's body). The problem of precisely striking a desired location on the Achilles tendon with an accurately reproducible amount of force has been solved, for example, by using a reflex hammer having a strike element, which is accurately positioned at the location on the tendon which is to be struck, and an impact member which is subjected to a predetermined, reproducible amount of momentum which is imparted to the strike element upon impacting therewith. For example, a simple, inexpensive reflex hammer which achieves reliable reproducability and utilizes an impact member which is dropped from a predetermined height above a strike element and impacts therewith is described in U.S. Pat. No. 3,626,927, issued to me on Dec. 14, 1971.
Known devices for measuring the reflex action of a patient in response to striking the Achilles tendon include simple mechanical devices, such as those comprising a lever, which is contacted by the patient's foot, and gears which mechanically link the lever with an indicating pointer operable over a dial to provide instantaneous readings of the amount of muscle contraction caused by striking the Achilles tendon. Such measuring devices do not provide a permanent record of the reflex action as a function of time, and are of very limited value for measuring the progress of a patient being treated for a particular disease or disorder which affects the reflexes.
Measuring devices which provide an electrical signal to a recording apparatus to generate a permanent record of reflex action as a function of time have generally been relatively complicated, expensive, and are less accurate than the simple mechanical measuring devices. Such measuring devices having a recordable electrical output include an electromagnetic field generator which is connected with a recording device to record fluctuations in the electromagnetic field caused by movement of a small permanent magnet attached to the patient's foot, which is generally positioned near the center of the electromagnetic field. The electromagnetic field measuring device does not provide an inherently accurate reading of muscle contraction and relaxation as a function of time because the disturbances caused by movement of a magnet through the electromagnetic field cannot be easily or directly correlated with the position of the magnet in the field. The device is also undesirable in view of recent findings which suggest that exposure to electromagnetic fields can be injurious to a person's health.
Another measuring device which is utilized to record reflex responses is a photoelectric detector. The photoelectric device is generally used by positioning the patient's foot so that it partially blocks a light beam directed at the photoelectric detector. The Achilles tendon of the patient is then struck causing the patient's foot to move further into the light beam, generating a change in the photocell voltage which is recorded. As with the electromagnetic field measuring device, the photoelectric device is relatively expensive and may not necessarily provide an accurate record of the position of the foot as a function of time after the Achilles tendon is struck, because the photoelectric detector is only responsive to the amount of light detected, which may not necessarily be directly related to the position of the foot in all cases. For example, errant light sources could interfere with the measurements, and the light beam directed at the photoelectric detector can be fully obscured before peak contraction of the muscle in response to striking the Achilles tendon, thereby making it difficult or impossible to accurately determine the time from peak contraction to when the muscle has relaxed to one-half of its peak contraction, a parameter which is commonly used to characterize reflex action, and used as an aid in diagnosing disease, prescribing treatment, and monitoring a patient's progress.
Another disadvantage with all of the known apparatuses for testing reflex action is that such apparatuses are designed for, and permit only, testing of one of the Achilles tendons at a time. An obvious benefit of testing both Achilles tendons at the same time is that testing can be completed more quickly. A more important, but perhaps less apparent, benefit of testing both tendons simultaneously is that it facilitates direct comparison between the left and right Achilles tendons under substantially identical conditions. Such direct comparisons can be useful for determining the extent of neurological damage caused by traumatic injury such as to only one of a patient's legs, and could serve as a method for early detection of medical disorders which would not ordinarily be expected to affect both Achilles tendons equally, especially during the onset of certain diseases. Accordingly, an apparatus which facilitates direct comparison of reflex action of left and right Achilles tendons under precisely identical conditions can provide early detection of medical disorders, thereby allowing early treatment which will generally minimize a patient's suffering and can, in some cases, minimize or eliminate any permanent damage to the patient. Such direct comparisons can also be beneficial to employers and insurance companies by providing a simple method by which preexisting medical conditions and/or disorders can be detected.
Sequential testing of the left and right Achilles tendons cannot provide direct comparison of the reflex actions thereof, even when performed within a very short interval of time such as within one minute, because a person's reflexes are affected by a wide variety of factors such as heart rate, respiratory rate, blood pressure, body temperature, etc. Moreover, the first test can, by itself, induce physiological and psychological effects which can influence subsequent testing.
In view of the known reflex testing apparatuses, there is a need for an Achilles tendon reflex testing apparatus which is capable of inducing a reflex action in both left and right Achilles tendons simultaneously, and which includes measuring devices for accurately measuring the reflex response of the muscles associated with the left and right Achilles tendons, respectively, and providing a recordable electrical output indicative of the measured reflex responses. Additionally, there is a need for a measuring device, for use with reflex testing apparatuses, which is capable of providing a recordable electrical output signal which is more accurately indicative of the reflexive muscle contraction and relaxation associated with striking an Achilles tendon, and which is relatively simple, reliable, and inexpensive as compared with known measuring devices which provide a recordable electrical signal indicative of a human reflex response.